A client is asking that we design a small addition to an existing building, and get the project LEED certified. Now, the existing building was not built very efficiently. The new addition will be, of course, but it is only 10% of the building footprint.

My question is: How do we figure the new building vs. old in calculating LEED points? For example, in energy modeling, does the entire building have to be better than ASHRAE 90.1, or just the new addition (there is no way the existing building could meet ASHRAE 90.1) In lighting credits, does the entire building have to be under so-many watts per square foot, or just the new addition? (the existing building would not meet the maximum watts/sft)

Much of the existing building is daylit - do we count the whole building when figuring daylighting, or just the new addition?

I told the client that if USGBC wants us to count the entire building, then they'd have an uphill battle getting the project certified. If only the new addition is counted, then it would be straightforward.